Migrate CallLogBackupAgentTest to JUnit4

This commit migrates `CallLogBackupAgentTest` from JUnit3 to JUnit4, improving compatibility and maintainability.

Changes include:
    - Removing inheritance from `AndroidTestCase`
    - Using JUnit4 annotations (`@Before`, `@After`, `@Test`)
    - Updating imports for JUnit4 assertions
    - Fixing casts in Mockito `verify()` calls

Flag: TEST_ONLY
Bug: 371959886
Test: `atest CallLogBackupAgentTest`
Change-Id: Ie7b21e595139a9dd1267a7956e9a2c71c4fa69c8